1) We were unable to detect Mo^a, Sr^a or Va^a antigens among Japanese using our platelet-panel. In contrast, about 5% (15/314) were found to be Tu^a positive.2) We have experienced 29 cases of NAIT (Neonatal Alloimmune Thrombocytopenia) : 20 cases due to anti-HPA-4b (YuK^a) antibodies, 3 cases due to anti-HPA-4a (Yuk^b), 5 cases due to anti-HPA-3a (Bak^a) and 1 case due to anti-HPA-5b (Br^a). Among them 3 cases were complicated with intracranial hemorrhage.3) By screening a large number of samples, we found that anti-HPA-2b (Sib^a) playd an important role in the case of platelet transfusion refractoriness.4) The MPHA (mixed passive hemagglutination) method was developed about 15 years ago as a simple and sensitive test for the detection of anti-platelet antibodies. It has been refined now. Using 5% sucrose, the platelet-fixed plate can be kept frozen (below-40 C) without loss of reactivities for more than a year. Thus, MPHA should be employed as the routine test in any lab in the hospital for the detection of platelet allo-antibodies.